T. N. Mogileva

Size effect on the optical limiting in suspensions of detonation nanodiamond clusters

We report on the optical limiting (OL) in stable aqueous suspensions of detonation nanodiamond (ND) clusters with average size of 50, 110, and 320 nm. The nanosecond Z-scan measurements at wavelength of 532 nm revealed that the larger the cluster size, the better the OL performance and the higher the ray stability of the ND suspension. Our analysis showed that the nonlinear scattering and the nonlinear absorption are the dominant mechanisms of OL in aqueous ND suspensions.

Nonlinear scattering of light in nanodiamond hydrosol

The nonlinear scattering of light under the conditions of optical limiting of nanosecond pulsed laser radiation at a wavelength of 1064 nm in a nanodiamond (ND) hydrosol has been experimentally studied. Superstable hydrosols were obtained from detonation NDs with a modified surface. Using an improved scheme of z scanning, it is shown that a decrease in the optical transmission coefficient of an ND hydrosol under optical limiting conditions is due to enhanced nonlinear scattering. It is established that the energy of pulsed radiation scattered at a right angle obeys a power law in dependence on the energy density of incident radiation pulses. Hydrosols of detonation NDs with the modified surface exhibit high stability with respect to the periodic laser action at high power density.

Laser modification of optical properties of a carbon nanotube suspension in dimethylformamide

It is shown experimentally that a semitransparent suspension of multiwall carbon nanotubes (MWNTs) in N,N-dimethylformamide (DMF) is irreversibly bleached in a wide optical wavelength range in a field of nanosecond high-power laser radiation with a wavelength of 532 nm. The bleaching is accompanied by a sharp decrease in the nonlinear scattering; the suspension ceases to optically limit power. It is shown that the suspension is bleached due to light-induced chemical reactions between MWNTs and DMF molecules with formation of new hydrocarbon chemical bonds.

The Effect of the Size Factor of Nanodiamonds in Suspensions on Optical Power Limiting and Nonlinear Laser Light Scattering

The results of experimental studies of optical power limiting (OPL) and nonlinear light scattering (NLS) at a wavelength of 532 nm in suspensions of detonation-synthesis modified nanodiamonds (MNDs) with different grain-size compositions are described. It is found that, at the same nanoparticle concentration, OPL and NLS are more efficient in suspensions with large MNDs. It is shown that MND suspensions can exhibit a stable long-term operation as OPL in a field of laser pulses with a power density of 0.2 GW/cm2 at a repetition frequency of 1 Hz.

Thresholds of optical limiting in solutions of nanoscale compounds of zinc phthalocyanine with galactopyranosyl radicals

The optical limiting (OL) of nanosecond laser pulses in solutions of newly synthesized dyes in dimethyl sulfoxide (DMSO) has been investigated. These dyes are compounds of zinc phthalocyanine (ZnPc) with D-galactopyranosyl radicals (Gal) located in the peripheral (p-GalZnPc) and nonperipheral (n-GalZnPc) positions with respect to the ZnPc macrocycle. Experiments have been performed using laser radiation with a wavelength of 532 nm, at which the optical absorbance of solutions of ZnPc, p-GalZnPc and n-GalZnPc dyes is four orders of magnitude lower than the absorbance in the peaks at wavelengths of 671, 680, and 701 nm, respectively. It is established that solutions of p-GalZnPc and n-GalZnPc in DMSO have a much lower OL threshold in comparison with ZnPc solution; the nonlinearity of p-GalZnPc solutions exceeds that of n-GalZnPc solutions. OL thresholds for the dyes under study in a wide concentration range are determined.

Laser-induced diamagnetism in suspension of onion-like carbon particles

It is experimentally established that the bleached fraction of a suspension of onion-like carbon (OLC) particles in N,N-dimethylformamide (DMF), which is clarified under the action of high-power pulsed laser radiation at λ = 1064 nm, is pushed out from inhomogeneous magnetic field. By changing the spatial arrangement of a permanent magnet relative to the point of laser action on the suspension, it is possible to control the direction of motion of the bleached fraction. The observed behavior can be explained by laserstimulated chemical reactions between OLC and DMF, which lead to the formation of a new substance with pronounced diamagnetic properties.

Photoinduced Transparency of a Suspension of Onion-Like Carbon Nanoparticles

We have observed the phenomenon of photoinduced transparency in a suspension of onion-like carbon (OLC) nanoparticles in N,N-dimethylformamide (DMF) under the action of high-power laser radiation (λ = 1064 nm). The OLC particles were prepared from detonation nanodiamonds (NDs) by means of high-temperature annealing in vacuum and then ultrasonically dispersed in DMF. Upon exposure to laser radiation, the optical density of the suspension significantly decreases in the visible and near-infrared range, but increases in the range of wavelengths below 400 nm.

A Single-Mirror Electromechanical Laser Scanning System

The design of a compact single-mirror electromechanical system for the two-dimensional scanning of a laser beam is described. The system developed allows a mirror to be deflected by an angle of >20° from the neutral position at an oscillation frequency of 120–130 Hz, which is close to the systems resonance frequency. The gain–frequency and frequency–frequency characteristics of the system have been investigated at different shapes of the control voltage. The system described is applicable to both a direct change in the laser-beam direction in space and the control of the position of a target exposed to laser radiation.

Z-scanning under monochromatic laser pumping: a study of saturatable absorption in a suspension of multiwalled carbon nanotubes

A system has been developed and designed based on a single-mode single-frequency passive Q-switched pulsed YAG : Nd3+ laser to investigate with high accuracy the nonlinear optical properties of a liquid placed in an optical cell with uncoated input windows. The efficiency of this system is demonstrated by examples of studying the saturable absorption of an aqueous suspension of multiwalled carbon nanotubes and the nonlinear absorption of a colour glass filter ZhS18 at a wavelength of 532 nm.

Shapes of laser radiation pulses modified by nonlinear scattering in aqueous suspension of carbon nanotubes

An improved scheme of z-scanning was used to study the parameters of nanosecond 1064-nm laser radiation pulses scattered at right angle under the conditions of optical limiting in an aqueous suspension of purified carbon nanotubes (CNTs). CNTs were synthesized by the electric-arc evaporation of graphite. It is established that the amplitude, shape, duration, and temporal position of the peak of scattered light pulses significantly depend on the laser radiation power density. The results agree with the mechanism of thermoinduced nonlinear scattering that is operative during the optical limiting of laser pulses in CNT suspensions.